The ending of the film The Angel Levine is slightly different from that of the original source material. In Malamud's short story, Manischevitz grasps at what he believes to be a black feather drifting down from the sky. In actual fact, it turns out to be nothing more than a snowflake.
In the 1970 movie, however, the black feather eludes Manischevitz's grasp completely. It just keeps drifting in the air, tantalizingly outside the old man's reach.
In both the original story and the film adaptation, Levine changes back into what he once was: an angel. In the movie, Manischevitz can't understand why he does this. After all, his wife Fanny is still a very sick woman, though Levine tells Manischevitz that she will live, something that Manischevitz understandably finds hard to believe.
In any case, Levine departs from Manischevitz's life, seemingly having done what he was sent to earth to do. But this is no consolation to Manischevitz, who still needs the angel as his wife's condition continues to deteriorate.
After a long and fruitless search for the angel, Manischevitz sees a black feather floating in the sky. Convinced that it belongs to Levine, he grasps at it several times, but without success. The symbolism here is difficult to avoid. Manischevitz needs the Angel Levine to come back and help his ailing wife, but he's gone, never to return. His work is done.